June 14, 2012

Climate Change Linked To Woolly Mammoth Decline

New evidence points to a dual conspiracy of climate change factors and hunting activities by early man that to drove the woolly mammoth to extinction between 4,000 and 10,000 years ago.

The gradual decline of the sub-Arctic giant was likely caused in part by global warming induced changes in habitat, according to a new report published by an American-led research team in Nature Communications this week. These changes included a decline in the mammoths' food sources, particularly grasses and willows, but encouraged the growth of potentially toxic birch along with the proliferation of unfriendly terrain in the form of marshy peatlands and thick forests.

"We were interested to know what happened to this species during the climate warming at the end of the last ice age because we were looking for insights into what might happen today due to human-induced climate change," said lead author Glen MacDonald, a UCLA scientist. "The answer to why woolly mammoths died off sounds a lot like what we expect with future climate warming."

Using 1,323 mammoth radiocarbon dates, 658 peatland dates, 447 tree dates, and 576 dates from Paleolithic archaeological sites, the scientists created a database along with information on hundreds of previously dated mammoth samples. The information allowed them to create a detailed map that told the story of the mammoth´s demise.

According to the data, most of the woolly mammoths died about 10,000 years ago, yet smaller populations lingered until about 4,000 years ago on islands like modern day Wrangel Island, located north of Siberia in the Arctic Ocean.

In addition to changes in climate and habitat, woolly mammoths were facing the threat of predation by early humans during this time. Both were known to inhabit the same regions and evidence of humans hunting bovine and horses that dates back 10,000 years ago has been found in southwestern Canada.

Previous theories about the mammoths' extinction tended to focus on only one factor: hunting, climate changes, disease or even climate-changing meteor impact. The new research marks the first time scientists mapped out and dated so many different aspects of the era at once.

"Glen's project combined paleobotanical, paleontological, genetic, archaeological and paleoclimate data and did it in a bigger way, with many more data points, than has been done before," said UCLA co-author Van Valkenburgh. "I was excited to be able to contribute to such an ambitious and exciting study."

The woolly mammoth study marks the second report this month that points to a confluence of climate change and human factors causing the demise of a species. In a study published last week, a two decade-long research project on extinct Australia megafauna found that a similar combination was responsible for the demise of animals like the giant koala.

Using similar dating techniques, the scientists were able to determine that climate change factors along with human activity altered the habitat of the giant birds and marsupials that once roamed the Australian interior. Fewer monsoon rains, human agriculture, and deforestation conspired to keep moisture from reaching the continent´s interior and doomed these now extinct species.

Image 2 (below): Woolly mammoth skull from the collection of the University of Alaska Museum, Fairbanks. Credit: Glen MacDonald